1. Field of the Invention
The present invention relates to a device for controlling an intake air quantity of a combustion engine, which controls the intake quantity in response to running conditions of a vehicle, and a method of producing the device.
2. Discussion of Background
A choke valve for a combustion engine of a vehicle is located in an intake passage of a throttle body, opened and closed in proportional to an amount of operating an accelerator, and operated upon, for example, detection of slipping by a difference between rotations of front wheels and rear wheels to control an output from the combustion engine by controlling an intake air quantity. Therefore, the choke valve is not directly connected to the accelerator by a linkage mechanism in order to open and close the choke valve. The choke valve is driven with a control of opening and closing positions by a motor and so on, and the opening and closing positions are determined by a composite signal including the signal concerning an amount of applying the accelerator.
FIG. 2 is a cross-sectional view of a part of a conventional intake quantity controlling device for a combustion engine. In FIG. 2, numerical reference 21 designates a housing of a throttle body, having an intake air controlling portion 23, having a diameter the same as that of an intake air passage 22 for supplying an intake air to the combustion engine, and a motor accommodating portion 25, both monolithically molded by same synthetic resins. Numerical reference 26 designates a valve shaft located in the intake air controlling portion 23 of the housing 21, supported by a bearing 27 at both ends so as to be rotatable, penetrating through the intake air passage 22, and having a choke valve 28. The choke valve 28 rotates and moves from a completely closed position to a fully opened position of the intake air passage 22 upon rotation of the valve shaft 26 so as to control an intake air quantity. To one end of the valve shaft 26, a decelerating mechanism driven by the motor 29 is coupled.
A stator 30 of the motor 29 is attached to the motor accommodating portion 25 of the housing 21 by inserting and molding. A rotator 32 has a driving shaft 31. Both ends of the driving shaft 31 are supported by bearings 33 and 34, located in the motor accommodating portion 25 of the housing. The driving shaft 31 is arranged in parallel with the valve shaft 26 and has a gear 31a at its tip.
Numerical reference 35 designates a decelerating gear comprising the decelerating mechanism. The decelerating gear decelerates rotation of the motor 29 in collaboration with other gears (not shown) to drive the valve shaft 26. Numerical reference 36 designates a sensor located in the vicinity of the coupled portion of the decelerating mechanism to the valve shaft 26. The sensor 36 detects a rotational angle of the valve shaft 26 in order to control a driving position of the motor 29. Numerical reference 37 designates a connector, monolithically molded with the housing 21 and integrally grouped so as to be externally connected with the sensor 36 and the motor 29. Numerical reference 38 designates a cover covering a driving portion of the valve shaft 26 between the valve shaft and the motor 29.
Since the conventional intake air quantity controlling device is constructed as described above, when the housing is made of a resin, a size of the housing is changed by a physical volume change by a temperature change after molding. Further, because of a difference of a rate of dimensional change with respect to a flowing direction at time of molding, there is a problem that a high technique and a management are necessary to enable a production achieving required stable accuracies of an inner diameter of the intake air passage, pitches of the decelerating portion, and so on. Further, because a strength of a resin is generally smaller than a strength of a metal, there is a problem that a specific shape is necessary to reinforce the strength.